Patent documents 1 discloses an ignition device provided with a microwave oscillation device as an apparatus so called an ignition coil (see FIG. 3). The microwave oscillation device has an amplification element. The head part of the ignition device is provided with a mounting flange (see FIG. 4). The ignition device is fixed to the internal combustion engine main body using an attachment bolt which penetrates the mounting flange.